Strength members, reinforcing members, and structural members made of metal are used in automobiles and various types of machinery. A high strength, a low weight, and a small size are demanded of these members. In the past, these members have been manufactured by welding of press worked steel parts, punching of thick steel plates, or forging of aluminum alloys. Decreases in the weight and size of bent members achieved by these manufacturing methods have reached a limit. In Patent Document 1, the present applicant disclosed a manufacturing apparatus for a bent member.
FIG. 12 is an explanatory view schematically showing that manufacturing apparatus 0. The manufacturing apparatus 0 manufactures a bent member 8 by bending a metal tube 1 (in the following explanation, an example will be given of the case in which the metal tube is a steel tube) which is supported by a support mechanism 2 so as to be able to move in its axial direction, the bending being performed on the downstream side of the support mechanism 2 while feeding the steel tube 1 from the upstream side to the downstream side with a feed mechanism 3.
On the downstream side of the support mechanism 2, an induction heating coil 5 rapidly carries out induction heating of the steel tube 1 being fed in the axial direction to a temperature range (to at least the Ac3 point) at which the steel tube 1 can be locally quench-hardened. A water cooling mechanism 6 rapidly cools the steel tube 1 immediately downstream of the induction heating coil 5. As a result, a high temperature portion 1a which moves in the axial direction of the steel tube 1 is locally formed in the steel tube. The resistance to deformation of the high temperature portion 1a is markedly lower than the resistance to deformation of other portions.
A movable roller die 4 has at least one roll pair 4a. The roll pair 4a supports the steel tube 1 while feeding it. In a region downstream of the water cooling mechanism 6, the movable roller die 4 moves two-dimensionally or three-dimensionally while supporting the steel tube 1, thereby applying a bending moment to the high temperature portion 1a of the steel tube.
In this manner, the manufacturing apparatus 0 manufactures a bent member 8 having a desired shape and a high strength (such as a tensile strength of at least 780 MPa) by bending the steel tube 1 with a high operating efficiency by simple steps using relatively inexpensive components 2-6.